1. Field of the Invention
The present invention relates to a laser processing device for processing a workpiece by irradiating a workpiece such as a semiconductor wafer with a pulsed laser beam.
2. Related Art
A wafer on which a plurality of devices such as IC and LSI are formed while being partitioned by predetermined division lines is divided into individual devices by a dicing device or a laser processing device to be used for electronic instruments such as mobile phone and a personal computer.
The thickness of wafer is set to be thin, such as about 100 μm to 50 μm, so as to achieve reduction in size and weight of an electronic device while a via hole (through hole) is perforated and provided on the rear surface of a bonding pad of device (for example, refer to JP-A-2003-163323). In the technology in JP-A-2003-163323, a fine via hole is formed by a drill, which is poor in productivity. Consequently, a technology of perforating and providing a via hole on the rear surface of the bonding pad of the device by a laser processing device has been devised and a patent application thereof is filed by the applicant of the invention as seen in JP-A-2006-247674 (corresponding to US 20060201920)
There are some laser processing devices for removing a low-dielectric-constant insulating film (Low-k film) laminated on predetermined division lines by irradiating the predetermined division lines of wafer with a laser beam, forming division grooves, and forming affected layers inside the predetermined division lines by irradiating the wafer with a laser beam having a wavelength with optical transparency (for example, refer to JP-A-2003-320466; JP-A-6-120334; JP-A-2002-192367), as well as perforating and providing the via hole.
However, in the case of perforating and providing a via hole by irradiating with a laser beam, although the position of laser beam irradiation is controlled by an X-Y-axis coordinate value to irradiate with a pulsed laser beam at a predetermined number, the laser beam is not sufficiently irradiated to leave the part that does not function as a via hole.
Also in the case of removing a low-dielectric-constant insulating film (Low-k film) by laser beam irradiation or forming division grooves and affected layers, the low-dielectric-constant insulating film is not properly removed due to discontinuous pulsed laser beam irradiation or a wafer is not property divided due to intermittent formation of the division grooves or the affected layers.
Such problems arise in the case where a laser beam irradiating unit does not irradiate with a pulsed laser beam at a preset pulse number actually or in the case where energy of pulsed laser beam per pulse is not uniform. In the conventional technique, the failure of laser processing device is recognized by checking the processed wafer to sacrifice the wafer, which is not economical.